Nthato Motlana, generally recognized as the popular leader of sprawling black township of Soweto, has been served with a one-month banning order, it was disclosed yesterday.

The banning order - which prohibits Motlana from attending any gathering and specifically any meeting at which principles of government are discussed or criticized - was handed to the 52-year-old physician Wednesday, hours before he was to address an audience at a university here.

Justice Minister Jimmy Kruger, in issuing the order, said he was satisfied that Motlana was engaged in activities that endangered maintenance of public order. Motlana is chairman of Soweto's Committee of 10, a self-appointed but widely supported alliance of black militants and middle-aged moderates working to improve conditions for the township's 1.5 million black residents.

Kruger brought no criminal charges against the black leader and provided no details on how he arrived at the finding that Motlana endangered public order.

The gagging of Motlana, respected by militant black youths but still willing to negotiate with white officials, is likely to increase bitterness in the black community against the South African government.

Moderate whites, especially academics outside the government who have been calling for more dialogue between whites and black leaders like Motlana who have a popular following, also criticized the banning.

Professor John Dugard, dean of the Law School at the University of Witwatersrand, called the order insane. He read Motlana's prepared speech to a packed hall.

Some political observers speculated that Kruger's move against Motlana was aimed not only at keeping the black leader out of the limelight, but also at blocking efforts by more moderate Afrikaners to start an exploratory dialogue with black leaders.

Such a meeting was planned last October by leading moderate Afrikaner writer Willem de Klerk, editor of the Afrikaans newspaper Die Transvaler. It was effectively blocked by an October 19 security clampdown, in which Motlana and 48 other black leaders were arrested.

The effort was renewed again last month when black leaders of varied political views, including Motlana, met with De Klerk and other Afrikaner business and academic leaders. The group had announced its intention to meet again in the near future. Motlana's banning order prevents him from taking part if the meeting is held before the end of this month. The order can be extended at will by Kruger.

Last June Kruger warned Motlana against making inflammatory speeches after the black leader addressed a commemorative ceremony on the second anniversary of the out-break of student protest in Soweto. Wednesday night's speech at the University of Witwatersrand would have been his first major public address since that warning.